This invention concerns sewage treatment processes, and in particular relates to scum removal in a clarifier.
In a typical conventional activated sludge sewage treatment process, a considerable volume of scum and other gross floatables enters with the influent feed into the clarifier basin. This is distinct from the biological scum which arises from biological processes occurring in the basin. In conventional clarifiers the influent scum and other floatables were often moved out of the influent well to be collected along with biological scum, over the entire clarifier surface or at the periphery of the clarifier. The two types of scum typically were commingled and discharged together, and where influent well scum and floatables were collected they were delivered to the periphery of the clarifier and commingled with biological scum.
Examples are the SS Clarifiers of Enviroquip, Inc., being of open trough design and having scum ports that move with the rake arms collecting scum and other floatables over the entire clarifier surface, with commingling. Although such systems function well to remove scum from the clarifier, a problem is the volume of water taken in with the scum--sometimes 200 to 300 gallons per minute, producing a very watery, diluted scum which would hydraulically overload the digester or sludge concentration area in the wastewater handling area.
Some prior clarifier systems have had influent wells that prevented egress of scum or gross floatables at the surface. Some have included a fixed scum beach or box within the influent well, with a rotating scrapper blade in the well for collecting surface scum and floatables onto the beach or box. Some clarifiers have incorporated rotating open scum troughs extending from center pier to the periphery of the clarifier with ports both inside and outside the influent well. However, even where the scum and floatables were sequestered and collected within the influent well, they were not handled separately from other biological scum for separate discharge and they were not discharged through the center pier.
The following U.S. patents were concerned with sewage treatment and clarifiers and have some relevance to the subject matter of this invention: U.S. Pat. Nos. 1,892,688, 2,295,982, 2,262,412, 2,506,927, 2,661,094, 2,681,151, 2,798,041, 2,801,007, 2,822,928, 2,875,697, 3,132,733, 3,166,502, 3,206,036, 3,216,570, 3,234,880, 3,314,547, 3,327,867, 3,770,131, 3,892,666, 3,926,805, 3,396,102, 3,487,017, 3,526,591, 4,193,877, and 5,219,470.
The prior art did not contemplate the efficient scum removal system of the present invention, in which virtually all scum and other floatables entering the clarifier's influent well are sequestered in the influent well, efficiently collected there in a nearly dry state, then discharged down the center pier and separately from other scum or sludge in the clarifier, for separate subsequent processing.